Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
International Journal of Current Microbiology and Applied Sciences
ISSN: 2319-7706 Volume 4 Number 2 (2015) pp. 981-993
http://www.ijcmas.com
Review Article
Targeting cyanobacteria as a novel source of biofuel
Pankaj Goyal*, Abhishek Chauhan and Ajit Varma
Amity Institute of Microbial Technology, Amity University Uttar Pradesh, Noida, U.P., India
*Corresponding author
ABSTRACT
Keywords
Cyanobacteria,
Biofuel,
Photosynthesis,
Oil Content,
Microbial Fuel
Cells.
Exploration of novel sources for the production of unconventional fuel i.e. biofuel
such as biohydrogen, bioethanol, biodiesel and biogas is of utmost prerequisite in
order to evade limited fuel assets, intensifying costs and of course, environmental
issues due to rising emissions of harmful gases from fossil fuel. Therefore,
significant considerations are given towards the biological conversion of carbon-dioxide and solar energy to biofuel in order to facilitate an economically sustainable
industrial society. Microalgae and cyanobacteria viz. Botryococcus braunii,
Chlorella, Dunaliella tertiolecta, Gracilaria, Pleurochrysis carterae, Sargassum
etc. are, in fact, matter of choice for biofuel production than that of plant biomass
because of higher oil content, oxygenic photosynthesis, higher growth rates and
per-acre productivity, fewer requirements for in vitro cultivation, non-food based
feedstock, growth on non-productive land and on different water sources like
freshwater, seawater, wastewater, production of valuable co-products and evidently
algal biofuel is free of sulfur, is non-toxic, and is highly biodegradable. Microalgae
contain approximately 2-40% lipids and fatty acids as membrane components,
storage products, metabolites and sources of energy. It has been estimated that
algae produces at least thirty times more energy per acre than land crops such as
soybeans, and some estimate even higher yields up to 15000 gallons per acre.
Moreover, these microbial fuel cells (MFCs) are relatively more convenient
organisms to carry out genetic engineering in order to produce metabolites which
are characteristically not produced by these organisms in nature. Producing
biodiesel from algae provides the highest net energy because converting oil into
biodiesel is much less energy-intensive than methods for conversion to other fuels
such as ethanol, methane etc. This characteristic has made Biodiesel the favorite
end-product from algae. Eventually, microalgae put forward the prospective to
have an insightful impact for the welfare of earth and society on several vital
concerns of alternative energy resources, global warming, human health and food
security.
Introduction
of first generation biofuels as environmentfriendly alternatives to foreign oil, primarily
In the recent past, there has been a lot of
discussion and interest around the viability
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Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
because of their possible competition with
food crops and the use of non-sustainable
practices for their production. Scientists and
research groups have been searching for
other sustainable sources for biofuel
production, and microalgae seem to be one
such alternative with a promising potential.
Metzger and Largeau, 2005; Singh et al.,
2005; Spolaore et al., 2006; Walter et al.,
2005). In addition, these photosynthetic
microorganisms are known to produce
intracellular and extracellular metabolites
with diverse biological activities such as
antibacterial (Falch et al., 1995; Mundt et
al., 2001; Rao et al., 2007; Kaushik and
Chauhan; Kaushik et al., 2009), antifungal
(MacMillan et al., 2002), cytotoxic (Luesch
et al., 2000), algaecide (Papke et al., 1997),
immunosuppressive (Koehn et al., 1992) and
antiviral activities (Hayashi & Hayashi,
1996; Kaushik and Chauhan, 2009).
Microalgae are a diverse group of
prokaryotic and eukaryotic photosynthetic
microorganisms that can grow rapidly due to
their simple structure (Kaushik and
Chauhan, 2009). They have been
investigated for the production of different
biofuels including biodiesel, bio-oil and biohydrogen. Microalgal biofuel production is
potentially sustainable. It is possible to
produce adequate microalgal biofuels to
satisfy the fast growing energy demand
within the restraints of land and water
resources.
Microalgae can provide several different
types of renewable biofuels. These include
methane produced by anaerobic digestion of
the algal biomass (Spolaore et al., 2006);
biodiesel derived from microalgal oil
(Roessler et al., 1994; Sawayama et al.,
1995; Dunahay et al., 1996; Sheehan et al.,
1998; Banerjee et al., 2002; Gavrilescu and
Chisti, 2005); and photobiologically
produced biohydrogen (Ghirardi et al., 2000;
Akkerman et al., 2002; Melis, 2002;
Fedorov et al., 2005; Kapdan and Kargi,
2006). The idea of using microalgae as a
source of fuel is not new (Sawayama et al.,
1995), but it is now being taken seriously
because of the escalating price of petroleum
and, more significantly, the emerging
concern about global warming that is
associated with burning fossil fuels
(Gavrilescu and Chisti, 2005).
Microalgae contain lipids and fatty acids as
membrane components, storage products,
metabolites and sources of energy. Algae
contain anywhere between 2% and 40% of
lipids/oils by weight. There is a greater
possibiltiy to extract the oil/diesel from
these natural resources. The advantages of
deriving biodiesel from algae include rapid
growth rates and high per-acre yield.
Furthermore, algal biofuel contains no
sulphur, is nontoxic, and is highly
biodegradable. Some species of algae are
ideally suited to biodiesel production due to
their high oil content in some species,
tapping out near 50%.
Between 1978 and 1996, the Aquatic
Species Program (ASP) focused on the
production of biodiesel from high lipidcontent algae growing in outdoor ponds and
using CO2 from coal-fired power plants to
increase the rate of algal growth and reduce
carbon emissions (Sheehan, 1998). Under
optimum growing conditions micro-algae
will produce up to 4 lbs./sq. ft./year or
15,000 gallons of oil/acre/year. Microalgae
They are sunlight-driven cell factories that
convert carbon dioxide to potential biofuels,
foods, feeds and high-value bioactives
(Metting and Pyne, 1986; Schwartz, 1990;
Kay, 1991; Shimizu, 1996, 2003;
Borowitzka, 1999; Ghirardi et al., 2000;
Akkerman et al., 2002; Banerjee et al., 2002;
Melis, 2002; Lorenz and Cysewski, 2003;
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Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
are the fastest growing photosynthesizing
organisms. They can complete an entire
growing cycle every few days.
approximately 50% carbon by dry weight
(Sanchez Miron et al., 2003). All of this
carbon is typically derived from carbon
dioxide. Producing 100 t of algal biomass
fixes roughly 183 t of carbon dioxide.
Carbon dioxide must be fed continually
during daylight hours. Feeding controlled in
response to signals from pH sensors
minimizes loss of carbon dioxide and pH
variations. Biodiesel production can
potentially use some of the carbon dioxide
that is released in power plants by burning
fossil fuels (Sawayama et al., 1995; Yun et
al., 1997). They can grow 20 to 30 times
faster than food crops. Algae can be
cultivated in open pond system and closed
loop system
Green fuel Technologies in Cambridge, MA
is field testing a closed system that uses the
CO2 in power plant flue gases (13% of flue
gases in the test) to feed algae (Novakovic,
2005). Greenhouses can be modified to
produce algae all year round. The surface
area limitation which applies to ponds could
be overcome in a greenhouse by adding a
third layer of plastic inside the other two
layers over which the pond water could flow
in a thin enough film that it would receive
enough solar radiation to grow algae.
Microalgae is, by a factor of 8 to 25 for
palm oil and a factor of 40 to 120 for
rapeseed, the highest potential energy yield
temperate vegetable oil crop.
Use of bioreactors
Provide fast growth of algae with the high
contents of oil. Photobioreactors have been
successfully used for producing large
quantities of microalgal biomass (Molina
Grima et al., 1999; Tredici, 1999; Pulz,
2001; Carvalho et al., 2006). The term is
more commonly used to define a closed
system, as opposed to an open tank or pond.
Because it is a closed system, the cultivator
must provide all nutrients, including CO2. A
photo bioreactor can operate in "batch
mode", which involves restocking the
reactor after each harvest, but it is also
possible to grow and harvest continuously.
Algae cultivation
Algae can produce 15-300 times more oil
per acre than conventional crops, such as
rapeseed, palms, soybeans, or jatropha, and
they have a harvesting cycle of 1-10 days,
which permits several harvests in a very
short time frame, increasing the total yield
(Chisti 2007). Algae can also be grown on
land that is not suitable for other established
crops, for instance, arid land, land with
excessively saline soil, and drought-stricken
land. This minimizes the issue of taking
away pieces of land from the cultivation of
food crops (Schenk et al. 2008). Water,
carbon dioxide, minerals and light are all
important factors in cultivation, and
different algae have different requirements.
The basic reaction in water is
Carbon dioxide + Light energy
Oxygen
Continuous operation requires precise
control of all elements to prevent immediate
collapse. The grower provides sterilized
water, nutrients, air, and carbon dioxide at
the correct rates. This allows the reactor to
operate for long periods. An advantage is
that algae that grows in the "log phase" is
generally of higher nutrient content than old
"senescent" algae. Maximum productivity
occurs when the "exchange rate" (time to
exchange one volume of liquid) is equal to
Glucose +
Temperature must remain generally within
20 to 30 °C. Microalgal biomass contains
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Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
the "doubling time" (in mass or volume) of
the algae.
work better for specific algae types. Many
commercial manufacturers of vegetable oil
use a combination of mechanical pressing
and chemical Solvents in extracting oil.
Harvesting
Algae can be harvested using microscreens,
by centrifugation, by flocculation (Bilanovic
et al., 1998) and by froth flotation.
Interrupting the carbon dioxide supply can
cause algae to flocculate on its own, which
is called "auto-flocculation". "Chitosan", a
commercial flocculent, more commonly
used for water purification, is far more
expensive. The powdered shells of
crustaceans are processed to acquire chitin, a
polysaccharide found in the shells, from
which chitosan is derived via de-acetylation.
Water that is more brackish, or saline
requires larger amounts of flocculent.
Flocculation is often too expensive for large
operations. Alum and ferric chloride are
other chemical flocculants. In froth flotation,
the cultivator aerates the water into a froth,
and then skims the algae from the top
(Gilbert et al., 1961) Ultrasound and other
harvesting methods are currently under
development (Bosna et al., 2003; US Patent
No. 6524486)
(b)
Ultrasonic-assisted
extraction:
Ultrasonic extraction, a branch of
sonochemistry, can greatly accelerate
extraction processes. Using an ultrasonic
reactor, ultrasonic waves are used to create
cavitation bubbles in a solvent material,
when these bubbles collapse near the cell
walls, it creates shock waves and liquid jets
that causes those cells walls to break and
release their contents into the solvent.
2. Chemical Methods: Algal oil can be
extracted using chemicals. Chemical
methods include:
(a) Hexane Solvent Method: Hexane
solvent extraction can be used in isolation or
it can be used along with the oil
press/expeller method. After the oil has been
extracted using an expeller, the remaining
pulp can be mixed with cyclo-hexane to
extract the remaining oil content. The oil
dissolves in the cyclohexane, and the pulp is
filtered out from the solution. The oil and
cyclohexane are separated by means of
distillation.
Extraction methods
1. Mechanical methods: The simplest
method is mechanical crushing. Since
different strains of algae vary widely in their
physical
attributes,
various
press
configurations (screw, expeller, piston, etc)
work better for specific algae types. Often,
mechanical crushing is used in conjunction
with chemicals. Mechanicals methods are of
two types:
(b) Soxhlet extraction: Soxhlet extraction
is an extraction method that uses chemical
solvents. Oils from the algae are extracted
through repeated washing, or percolation,
with an organic solvent such as hexane or
petroleum ether, under reflux in special
glassware.
3. Supercritical fluid Extraction: In
supercritical fluid/ CO2 extraction, CO2 is
liquefied under pressure and heated to the
point that it has the properties of both a
liquid and a gas, this liquified fluid then acts
as the solvent in extracting the oil.
(a) Expression/Expeller press: Algae is
dried it retains its oil content, which then
can be "pressed" out with an oil press. Since
different strains of algae vary widely in their
physical
attributes,
various
press
configurations (screw, expeller, piston, etc)
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by the company. Regional production of
microalgae and processing into biofuels will
provide economic benefits to rural
communities. Other sources of commercial
biodiesel include canola oil, animal fat, palm
oil, corn oil, waste cooking oil (Felizardo et
al., 2006; Kulkarni and Dalai, 2006), and
jatropha oil (Barnwal and Sharma, 2005).
Algal fuels
The algae product can then be harvested and
converted into biodiesel; the algae’s
carbohydrate content can be fermented into
Biofuel.
Biodiesel
Microalgae have a large capacity for
producing lipids for biodiesel and
carbohydrates for bioethanol. The potential
for microalgae as biofuel feedstocks is high
because of their high rate of productivity,
the potentially high percentage of biomass
composed of lipids or carbohydrates, and
because they lack lignin. The absence of
lignin production in most algae is a benefit
because processing lignin is currently a
major impediment for bioethanol production
(Moore, 2009).
Lipids from various sources can be
converted to biodiesel through the process of
transesterification (Chisti 2007). Microalgae
provide an excellent source of lipids for two
major reasons. First, microalgae productivity
can be an order of magnitude greater than
terrestrial vegetation used for biofuel
feedstocks. Second, the lipid content of
microalgae can exceed 70% of their dry
mass, although algae with lipid content of
around 30% is more common (Chisti 2007).
High productivity combined with high lipid
content results in a large amount of lipid that
can be harvested annually for biodiesel
production.
Producing biodiesel from algae provides the
highest net energy because converting oil
into biodiesel is much less energy-intensive
than methods for conversion to other fuels
(such as Ethanol methane etc). This
characteristic has made Biodiesel the
favorite end-product from algae. Producing
biodiesel from algae requires selecting highoil content strains, and devising cost
effective methods of harvesting, oil
extraction and conversion of oil to biodiesel.
In addition to utilizing the lipids and
carbohydrates from microalgal biomass for
biofuel production, it is also possible to
make use of the other compounds present in
microalgal biomass. Microalgal proteins can
be use for fish feeds in aquaculture or
animal feeds for livestock and poultry
(Meng et al. 2009). Algae are currently
grown commercially to produce profitable
chemicals, such as antioxidants and dietary
supplements.
Studies show that algae can produce up to
60% of their biomass in the form of oil.
Because the cells grow in aqueous
suspension where they have more efficient
access to water, CO2 and dissolved
nutrients, microalgae are capable of
producing large amounts of biomass and
usable oil in either high rate algal ponds or
photobioreactors. This oil can then be turned
into biodiesel which could be sold for use in
automobiles. The more efficient this process
becomes the larger the profit that is turned
These chemicals comprise only a minor
component of the microalgae cells, but have
a high enough value to make their
production profitable (Rosenberg et al.
2008). The cost of producing bioethanol and
biodiesel from microalgae can be reduced by
exploiting every component of microalgae
biomass.
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Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
Fermentation
process:
Fermentation
process to produce ethanol include the
following stages:
Transesterification of Oil into Biodiesel
According to Y. Chisti (2007) parent oil
used in making biodiesel consists of
triglycerides (Fig.2) in which three fatty acid
molecules are esterified with a molecule of
glycerol. In making biodiesel, triglycerides
are reacted with methanol in a reaction
known as transesterification or alcoholysis.
Transestrification produces methyl esters of
fatty acids, that are biodiesel, and glycerol
(Fig. 2). The reaction occurs stepwise:
triglycerides are first converted to
diglycerides, then to monoglycerides and
finally to glycerol.
1. Growing starch-accumulating, filamentforming, or colony-forming algae in an
aqua culture environment;
2. Harvesting the grown algae to form a
biomass;
3. Initiating decay of the biomass;
4. Contacting the decaying biomass with a
yeast capable of fermenting it to form a
fermentation solution; and,
5. Separating the resulting ethanol from the
fermentation solution.
Other algae fules: Biogasoline, Methane
Straight Vegetable Oil, Hydrocracking to
traditional transport fuels and Jet Fuel are
produced from algae.
Transesterification of Oil into Biodiesel
Transesterification is catalyzed by acids,
alkalis (Fukuda et al., 2001; Meher et al.,
2006) and lipase enzymes (Sharma et al.,
2001). Alkali-catalyzed transesterification is
about 4000 times faster than the acid
catalyzed reaction (Fukuda et al., 2001).
Biodiesel is recovered by repeated washing
with water to remove glycerol and methanol.
Oil yields: The table-4 below presents
indicative oil yields from various oilseeds
and algae.
Advantages of biofuel production
Biofuel production using microalgal farming
offers the following advantages
Ethanol from algae
Ethanol from algae is possible by converting
the starch (the storage component) and
Cellulose (the cell wall component). Put
simply, lipids in algae oil can be made into
Biodiesel while the carbohydrates can be
converted to ethanol.
(1) The high growth rate of microalgae
makes it possible to satisfy the massive
demand on biofuels using limited land
resources without causing potential
biomass deficit.
(2) Microalgal cultivation consumes less
water than land crops.
(3) The tolerance of microalgae to high
CO2 content in gas streams allows highefficiency CO2 mitigation.
(4) Nitrous oxide release could be
minimized when microalgae are used
for biofuel production.
(5) Microalgal farming could be potentially
more costeffective than conventional
farming.
Algae are the optimal source for second
generation Bioethanol due to the fact that
they
are
high
in
carbohydrates/polysaccharides and thin
Cellulose walls. Some prominent strains of
algae that have a high carbohydrate content
and hence are promising candidates for
ethanol
production
are
Sargassum,
Glacilaria, Prymnesium parvum, Euglena
gracilis.
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Table.1 Oil content of some microalgae (Adopted from Y. Chisti, 2007)
S. No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Microalgae
Botryococcus braunii
Chlorella sp.
Crypthecodinium cohnii
Cylindrotheca sp.
Dunaliella primolecta
Isochrysis sp.
Monallanthus salina
Nannochloris sp.
Nannochloropsis sp.
Neochloris oleoabundans
Nitzschia sp.
Phaeodactylum tricornutum
Schizochytrium sp.
Tetraselmis sueica
Oil Content (% Dry Wt)
25–75
28–32
20
16–37
23
25–33
>20
20–35
31–68
35–54
45–47
20–30
50–77
15–23
Source: Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing ,
China (2004)
Table.2 Lipid content of different algae
S. No.
1
2
3
4
5
6
7
8
9
Strains
Chlorella sp.
Scenedesmus sp.
Chlamydomonas sp.
Euglena sp.
Spirogyra sp.
Dunaliella sp.
Synechoccus sp.
Prymnesium sp.
Porphyridium sp.
% Lipid (on a Dry Basis)
14 - 22
12 - 40
21
14 - 20
11 - 21
6-8
11
22 - 38
9 - 14
Table.3 Comparison of biodiesel from microalgal oil and diesel fuel
S. No
Properties
1
2
3
4
5
6
7
8
Density Kg l-1
Viscosity Pa s
Flash point ºC
Solidifying point ºC
Cold filter plugging point ºC
Acid value mg KOH g-1
Heating value MJ kg-1
HC ratio
Biodiesel from
Microalgal Oil
0.864
5.2×10-4 (40 ºC)
65-115*
-12
-11
0.374
41
1.18
Based on data from multiple sources
987
Diesel Fuel
0.838
1.9 - 4.1 ×10-4 (40 ºC)
75
-50 – 10
-3.0 (- 6.7 max)
0.5 max
40 – 45
1.18
Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
Table.4 Comparison of average oil yields from algae with that from other oilseeds
S. No.
Oilseeds and Algae
Gallons of Oil per Acre per Year
1
2
3
4
5
6
7
Corn
Soybeans
Safflower
Sunflower
Rapeseed
Oil Palm
Microalgae
18
48
83
102
127
635
5000-15000
Fig.1 Biodiesel making
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Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
Fig.1 Technological circuit of installation of a bioreactor
WAT
ER
ALGA
E
CO
2
NUTRIEN
TS
FEEDING VESSEL
PHOTOBIOREACTOR
CENTRIFUGE
DRYER
OIL PRESS
ALGAE
OIL
PRESS
CAKE
Fig.2 A detailed process of biodiesel from algae
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Int.J.Curr.Microbiol.App.Sci (2015) 4(2): 981-993
The potential benefits of large-scale
production of microalgae for biofuels and
other products far outweigh the existing and
potential issues associated with microalgae
production. At the moment, microalgae
appear to be the best option for biofuel
feedstocks because of their tremendous
productivity, ability to use waste products in
their production, and the valuable
byproducts that can be produced. Research
dealing with improving production systems,
identifying ideal microalgae for biofuel
production,
and
investigating
the
sustainability of microalgal biofuel is
necessary before large-scale microalgal
biofuel
operations
are
established.
Microalgal biotechnology appears to possess
high potential for biodiesel production
because a significant increase in lipid
content of microalgae is now possible
through heterotrophic cultivation and
genetic engineering approaches. Keeping in
view the advantages of microalgae, the
study can be designed to develop the
technologies for the production of biodiesel
from microalgae, including the various
modes of cultivation for the production of
oil-rich microalgal biomass, as well as the
subsequent downstream processing for
biodiesel production.
Disadvantages of biofuel production
On the other hand, one of the major
disadvantages of microalgae for biofuel
production is the low biomass concentration
in the microalgal culture due to the limit of
light penetration, which in combination with
the small size of algal cells makes the
harvest of algal biomasses relatively costly.
The large water content of harvested algal
biomass also means its drying would be an
energy-consuming process. The higher
capital costs of and the rather intensive care
required by a microalgal farming facility
compared to a conventional agricultural
farm is another factor that impedes the
commercial implementation of the biofuels
from microalgae strategy. Nevertheless,
these problems are expected to be overcome
or minimized by technology development.
Given the vast potential of microalgae as the
most efficient primary producers of biomass,
there is little doubt that they will eventually
become one of the most important
alternative energy sources. Another problem
that arises in microalgae production is that
the algae-culture systems can easily and
quickly be contaminated with other
organisms (Zittelli et al. 2006). Species of
algae other than the target species can be
introduced to the production system and
compete with the target species. This
presents a problem because the overall
productivity of the system can be reduced.
One way to avoid the issue of contamination
is to grow microalgae that flourish under
extreme
conditions.
For
example,
Arthrospira maxima grow at very high pH
(9.5-11), while Tertraselmis grow in
extremely saline waters (Dismukes et al.
2008). Another method for avoiding
contamination is to grow the microalgae in a
closed system, under very controlled
conditions. There, however, is no guarantee
that contamination will not occur.
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